This invention relates to information transmission systems and in particular to infrared information transmission systems having multiple transmitter units.
The use of remote control units to transmit information and thus eliminate cumbersome hard-wire connections between transmitter and receiver is known in the art. Transmitting information using infrared signals has proved invaluable for shortrange communication and for eliminating mutual interference with radio frequency signals. An infrared information transmission system is described in U.S. Pat. No. 3,927,316 in which frequency modulated infrared signals from a wideband FM transmitter are received by a wideband receiver and transmitted to a speaker system. Another infrared transmission system is described in copending U.S. Pat. No. 4,150,284. In this system, information is transmitted as a series of modulated infrared pulses from a remote transmitter unit to a receiver module where the pulses are processed and decoded. The remote transmitter unit contains a keyboard and joystick for inputting information.
Hertofore, prior art infrared information transmission systems have required separate circuitry for processing and decoding information from each transmitter. In addition, the frequencies at which the infrared signals are transmitted are unduly susceptible to interferece from 60 Hz and broadband noise. Furthermore, when portable transmitter units are employed, the power supply must be frequently recharged or replaced because the system continues to experience power drain when activated even if no information is being transmitted.